A mobile node (hereinafter MN) using mobile IP (see Non-Patent Document 1 cited below, which is also called CMIP (client mobile IP)) registers a care-of address (Hereinafter CoA) as a destination address with a home agent (hereinafter HA) managing its home address (HoA) or with a correspondent node (hereinafter CN) to make a request for forwarding of packets destined to the HoA. If the MN can register two or more CoAs at the same time in association with one HoA, the MN having multiple interfaces will register a CoA assigned to each interface with the HA or the like to enable instantaneous switching from one CoA to another to be used according to the state of each individual interface. In Non-Patent Document 2 cited below, a technique in which the MN registers, with the HA, multiple CoAs in association with one HoA is described. Further, in proxy mobile IP (see Non-Patent Document 3 cited below, which is abbreviated as PMIP), since a MAG (Mobility Anchor Gateway) as a proxy node of the MN updates MN position information in place of the MN, the MN does not need to perform mobility management.
In 3GPP (Third Generation Partnership Project), a method of using a cell-phone unit (UE: User Equipment) provided with both a 3GPP interface (to be connected to a 3GPP network) and a WLAN interface or a WiMAX interface (to be connected to a Non-3GPP network) has been contemplated (Non-Patent Document 4) to enable the UE to hand over between the 3GPP network and the Non-3GPP network. The 3GPP network is a home network for the UE. In the network, a PDN gateway (hereinafter P-GW) exists as a gateway located between the network and a PDN (Packet Data Network) to provide various services to the UE, playing a role as a home agent for forwarding packets destined to the UE. The UE to be attached to the 3GPP network and the P-GW are connected by a connection established by GTP (General packet radio service Tunneling Protocol) or PMIP (Proxy Mobile IP) through a serving gateway (hereinafter S-GW). The UE generates an IP address from a home network prefix (hereinafter HNP) assigned from the P-GW, and uses the IP address as a home address (HoA). At this time, the S-GW has a role as the proxy node of the UE.
On the other hand, when the UE hands over from the 3GPP network to attach to the Non-3GPP network, if the Non-3GPP network is a trusted network (Trusted Non-3GPP network), the UE and the P-GW are connected by a connection established by PMIP or CMIP or MIPv4 through an AGW (Access Gateway), while if the Non-3GPP network is an untrusted network (Untrusted Non-3GPP network), they are connected by PMIP or CMIP through an ePDG (evolved Packet Data Gateway).
When PMIP is used in the Non-3GPP network, since HNP is assigned in an Attach Procedure performed with the AGW or the ePDG upon attachment to the network, the same address as that used upon attachment to the 3GPP network can be continuously used.
On the other hand, when CMIP is used in the Non-3GPP network, since a care-of address is assigned from the AGW or the ePDG, the UE sends a binding update (BU) message to the P-GW existing in the 3GPP network to associate the care-of address with the home address in order to generate a connection. Like in the case of PMIP, the home address (HoA) when CMIP is used in the Non-3GPP network is automatically generated using a HNP assigned in the Attach Procedure performed upon attachment to the Non-3GPP network. Since the assigned HNP is a value unique to each UE, the UE can generate any address other than the HoA from the HNP. This address other than the HoA is called the HNP address below.
Since the P-GW determines whether a packet is destined to the UE based on whether the destination address of the packet is the address generated from the HNP, all packets destined to the address generated by using the HNP are handled as packets destined to the UE. Therefore, the packets destined to the HNP address are forwarded to the UE according to a binding cache (BC) for the HoA in the same manner as the packets destined to the HoA. For example, when an address acquired in the Non-3GPP network is registered as a CoA, the CoA is also used by the P-GW as the forwarding destination of the packets destined to the HNP address.
In 3GPP, a case where the 3GPP interface and the Non-3GPP interface of the UE are connected to the respective networks at the same time has also been contemplated. In this case, since the UE and the P-GW use two interfaces at the same time, either the 3G interface side or the Non-3G interface side can be selected according to the type of a flow forwarded to the UE, enabling efficient use of a band for each connection. When CMIP is used on the Non-3GPP side and the connection destination of both interfaces is the same P-GW, the UE can use the same home prefix. In this case, the P-GW holds two BCs, i.e., a BC (HoA-CoA) (hereinafter, foreign binding), in which the CoA is associated with the HoA as a care-of address, and a BC (HoA-HoA) (hereinafter called home binding), in which the HoA is associated with the HoA as a care-of address. The foreign binding indicates the Non-3GPP interface of the UE as a forwarding destination, while the home binding indicates the 3GPP interface of the UE as the forwarding destination.
If these two BCs are registered with the P-GW, the P-GW can select either the 3GPP side or the Non-3GPP side as the forwarding destination of packets destined to the UE. The determination of which to select is made according to a routing rule for the UE. The routing rule can be defined and registered by the UE, or defined by an operator as well. Handling of the HNP address upon simultaneous connections is the same as that of the above-mentioned HNP address, and the BC for the HoA is also applied to the HNP address. Further, in this case, the routing rule registered for the HoA is also taken over together with the BC. Therefore, for example, when a routing rule for flows of a video conference between the UE and a CN, which indicates that audio flows are forwarded to the Non-3GPP side and video flows are forwarded to the 3GPP side, is registered with the P-GW, audio flows and video flows destined to the HNP address as well as audio flows and video flows destined to the HoA are forwarded according to the same routing rule.